Fine tuning of the size of CdS nanoparticles synthesized by a photochemical method

Abstract

In this work, we propose a combined photochemical–chemical methodthat enables us to grow CdS nanoparticles with ångström precision. CdSnanoparticles were formed through a photo-induced reaction betweenCdSO4 andNa2S2O3.Thioglycerol (C3H8O2S) was used as the capping agent. Fine tuning of the size was subsequently carried out bycontrolling the pH of the solution. Optical absorption spectroscopy was mainlyused to monitor the process of particle formation, and to measure the bandgapand size. X-ray diffraction spectra confirmed the optical sizes and demonstratedcrystalline nanoparticles. In the presence of the capping agent there was a darkgrowth that was completely dependent on the pH of the solution. The rate ofdark growth decreased when the pH of the solution increased to 7.0. In pHs of7.5 and 8, we observed a boundary situation where the number of particles wasconstant and only the existing particles grew in size. We proposed a model toexplain this effect. The model is based on the formation of a local higherH+ concentration near the nanoparticle’s surface. Finally, in pHs higher than 8.3 there was no dark growth.In a typical procedure, we showed that fine tuning of the size with ångström precision is possible, i.e. a1.6 Å change in size was obtained in 45 min reaction time.